**What Exactly Does A CIS Tester Test For??**
 

Hello everyone. I was wondering when purchasing a CIS tester, can this tester test for faulty injectors or a problem with the Fuel Distributor?? Can someone let me know what exactly the IS testers test for? thanks in advance!!!

Three components to a CI$ tester, dual pressure gauges, bypass valve, adapters to match fuel line fittings.

CI$ is pressure operated, testing is checking various combinations of pressures to meet spec. If they are correct depending on the problem the failing device is usually obvious. First step, check the pressures.

thanks!!!

The CIS tester cannot tell you if an injector is bad. It measures system and control pressures only. The system pressure is regulated by the relief valve in the fuel distributor and the control pressure is regulated by the WUR. If both of these are in range, final A/F adjustment is made with the hex screw adjuster in the lower plenum. Simplified, the fuel to the injectors is set by the difference between system (higher) and control (lower) pressure as adjusted by the air sensor plates movement of the center piston in the fuel distributor. If either pressure is out of range, external factors should be checked before replacing components. Plugged filters/screens, bad relief valve o rings, low pump pressure, and plugged return line are all examples of problems that could affect the pressures.

True that, you can easily check a bad injector by checking the spark plugs. It's how I found one not working on my Euro. Dry and clean plug = bad injector

A dry and clean sparkplug indicates a plugged injector. A partially plugged injector will normally show signs of blistering on the plug insulator due heat and preignition from lean running. A couple applications of Techron or Gumout injector cleaner will normally fix this.

CIS Injectors are not normally cleaned as they don't back clean very well. I did the "hold" the pintle open and spray cleaner through the output without very good results. This is why reputable places like Witchhunter don't even touch them. Plus, they are so inexpensive, why bother. Put some carb cleaner in the input side and use a compressor to push the fluid through, this will also clean plus show if the pattern is good. If one or two are bad, just replace with like injectors. The easiest is to just replace all with the MB ones. Trying to save 30 year old mechanical injectors really isn't worth it.


Just my opinion and experience.

MPDano,

I've had good luck cleaning them by letting them soak in cleaner then forcing the cleaner through them with at least 60 psi of air pressure to open the pintle. Sometimes I have to repeat this 2 or 3 times before getting a good conical spray pattern.

Always good to have lots of options. :cool:

awesome info guys! i appreciate all that was posted!